Duct shield



G. C. DEAKE May 24, 1932.

DUCT SHIELD Filed June 14, 1928 t 7 g. a

MA TTORNE y Patented May 24, 1932 PATENT FFEQE GEORGE O. DEAKE, OF BRONX, NEW YORK, ASSIGNOR, BY MESNE ASSIGNMENTS, TO METROPOLITAN DEVICE CORPORATION, A CORPORATION OF NEW YORK DUCT SHIELD Application filed June 14,

Where electric cables pass out of the ends of ducts into 'a manhole or similar open space, there is considerable attrition between the duct wall or lining and the lead sheath 6 of the cable. It is customary to provide at this point what is called a fairleader or shield of Zinc or lead between the cable and the wall or lining of the duct to avoid injury to the sheath. The present invention provides an improved shield for this purpose.

The accompanying drawings illustrate one embodiment of the invention.

Fig. 1 is a plan showing cable entering a manhole, part of the wall being shown 5 in section;

Fig. 2 is a vertical, longitudinal section of the same on a larger scale;

Fig. 3 is a longitudinal cross-section further enlarged;

Fig. 4 is a perspective View of the shield before application.

Conduits are built usually with a number of ducts entering a manhole into which the ends of cables are drawn for splicing or other connections. In Fig. 1, for simplicity, a single duct 1 is shown opening into one side of a manhole 2. A cable 3 leads out of the duct into the manhole where it is bent in various ways. WVhen the cable is carrying current, it is heated and expanded. As the current is cut off or varied, there is a movement of the cable further out of or back into the duct, with a tendency to seriously abrade the lead sheath of the cable against the edge of the wall around the duct. To avoid such abrasion.v a shield indicated at 4 is arranged around this portion of the cable.

The shield is made of a rectangular strip of heavy asbestos cloth as shown in Fig. 4:. This is wrapped around the cable with its opposite end portions 5 and 6 overlapping as shown in Fig. 3 on the underside of the cable, where the strain is greatest by reason of the weight. Snap fasteners 7, 7, 8 and 8 near the outer edge are sufficient to hold the shield in tubular shape. Preferably, also, the outer ply 6 carries fastened to it a curved plate 9 of zinc or other metal sufiiciently long to overlap the edge of the concrete as shown in Fig. 2 so as to reinforce the fabric and pre- 1928. Serial No. 285,264.

vent the corner of concrete from cutting through the fabric.

The shield approximately fills the conduit as shown in Fig. 3. I have found that asbestos cloth tends to adhere with its outer face to the duct wall and to let the lead sheath of the cable slip over it almost as eas ily as if its inner face were lubricated. The adhesion of the shield to the duct wall is particularly noticeable where this wall is of concrete. that is, without any of the lining materials sometimes used, such as steel, fibre or tile. The adhesive tendency may be increased by coating the outside face of the shield with a coating of sticky or adherent compositions, such, for example, as rubber.

The conditions in such locations are usually corrosive, by reason of the dampness and heat, and the only materials heretofore used for shields have been non-corrodible metals like zinc and lead. But in practice, it has been found that such shields tend to creep out of the duct and ultimately fall out of place leaving the cable unprotected. This is probably due to the frictional engagement with the cable sheath which at each expansion pushes the shield out a little more, engagement with the edge of the duct preventing the return of the shield when the cable contracts. The asbestos cloth of this invention, even where it contains the usual small percentage of cotton fabric. is practically unaffected by dampness or heat. It has a high resistance to abrasion and there is almost no friction between it and the lead sheath though it adheres tenaeiously to the duct wall. By test, it has been found to be substantially as durable as the zinc plates heretofore used and practically free from the tendency to creep out of the duct. And it is as good as or better than the standard zinc shields in the matter of wear on the lead sheath of the cable.

The fasteners at the end of the asbestos strip are not essential, but are advantageous in holding the overlapping plies in position. The zinc plate 9 may also be dispensed with, though it is advantageous in preventing cutting through the fabric. The use of a strip which can be wrapped about the cable makes ill) the application of the shield very easy. But the shield can be woven or otherwise made into a tube fitting loosely about the cable; in which case, it has to be threaded over the 5 end of the cable.

Various modifications may be made by those skilled in the art without departing from the invention as defined in the following claims.

What I claim is 1. A duct end shield for cables comprising a strip of asbestos material having at each end, complementary fastening means positioned so that the ends may be overlapped for an appreciable distance and fastened, and a piece of sheet metal interposed between the overlapping ends.

2. In combination a duct, a cable in the duct and protruding from the end thereof,

a shield interposed between the cable and the duct and extending beyond the edge of the duct, the shield comprising a two ply thickness of asbestos material and a piece of sheet metal interposed between the plies.

5 3. The combination of claim 2 in which the plies of asbestos are the overlapped ends of a strip of asbestos loosely surrounding the cable.

4. A duct end shield for cables comprising a strip of asbestos material having at each end fastening means whereby said strip may encircle a cable, and a piece of stiffening and strengthening material positioned in said shield to resist cutting against a sharp edge of a duct.

5. In combination, a duct, a cable in the duct and protruding from the end thereof. a shield interposed between the cable and the duct and extending beyond the edge of the duct, the shield comprising a sheet of asbestos material and a piece of stiffening and strengthening material mounted therein between the duct edge and the cable and extending inwardly and outwardly of the edge of said duct.

6. In combination, a duct, a cable in the duct and protruding from the end thereof, a shield interposed between the cable and the duct and extending beyond the edge of the duct, the shield comprising a two-ply thickness of asbestos material, and a piece of stiffening and strengthening material interposed between the plies.

In witness whereof I have hereunto signed my name.

- GEORGE C. DEAKE. 

